Control of an open-loop hydraulic offshore wind turbine using a variable-area orifice

Abstract

The viability of offshore wind turbines is presently affected

by a number of technical issues pertaining to the gearbox and

power electronic components. Current work is considering the

possibility of replacing the generator, gearbox and electrical

transmission with a hydraulic system. Efficiency of the

hydraulic transmission is around 90% for the selected

geometries, which is comparable to the 94% expected for

conventional wind turbines. A rotor-driven pump pressurises

seawater that is transmitted across a large pipeline to a

centralised generator platform. Hydroelectric energy

conversion takes place in Pelton turbine. However, unlike

conventional hydro-energy plants, the head available at the

nozzle entry is highly unsteady. Adequate active control at the

nozzle is therefore crucial in maintaining a fixed line pressure

and an optimum Pelton turbine operation at synchronous speed.

This paper presents a novel control scheme that is based on the

combination of proportional feedback control and feed forward

compensation on a variable area nozzle. Transient domain

simulation results are presented for a Pelton wheel supplied by

sea water from an offshore wind turbine-driven pump across a

10 km pipeline.